U.S. Democratic presidential candidate Hillary Clinton will not be campaigning in the western state of California Monday or Tuesday after being diagnosed with pneumonia.

A spokesman announced late Sunday she would not be making the previously planned trip, which was due to include fundraisers and a speech about the economy.

The Clinton campaign said a doctor had examined her Friday because of a prolonged cough. It was at that time that she was told she had pneumonia. Doctors gave Clinton antibiotics and advised her to rest and modify her schedule.

WATCH: Video footage of Clinton after leaving 9/11 ceremony

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But the diagnosis was not made public until Sunday after she appeared unsteady at a September 11 commemoration ceremony in New York. She left the event abruptly and a video showed her being helped by several people before she stumbled off a curb and got into a van.

Clinton's doctor said later she had become "overheated and dehydrated" but was "recovering nicely."

The 68-year-old candidate later emerged from her daughter Chelsea's apartment where she waved to supporters.

"I'm feeling great. It's a beautiful day in New York," Clinton said as she left in her car.

Republican presidential candidate Donald Trump, center, arrives to attend a ceremony at the National September 11 Memorial, in New York, Sept. 11, 2016, on the 15th anniversary of the Sept. 11 attacks.

Trump reacts

With the U.S. presidential election about two months away, the issue of Clinton's health is likely to linger.

A big part of that will be her Republican opponent, Donald Trump, who has cast Clinton as lacking the stamina necessary to handle the job.

He said Monday in an interview with Fox News that he hopes Clinton gets well, and that he plans to release the results of a physical exam he had during the past week.

"I hope she gets well and gets back on the trail and we'll be seeing her in the debate," Trump said.

The 70-year-old Trump released a letter from a physician late last year claiming he would be "the healthiest individual ever elected to the presidency."

But the doctor has since acknowledged he dashed off the note in five minutes while a Trump campaign limousine waited nearby.